As shown in FIG. 1, a conventional underwater detection device 1 receives an echo of an ultrasonic wave transmitted underwater from a ship bottom, and displays based on the received echo level, etc. Such an underwater detection device 1 typically includes a calculation module 500, a transmission module 100, a transmission/reception switching module 200, a transducer 300, a reception module 400 and a display module 600. Hereinafter, the detection and display method of the underwater detection device 1 will be explained.
First, the transmission module 100 amplifies a transmission drive signal. The transmission drive signal is applied to the transducer 300 through the transmission/reception switching module 200, and the module 200 then transmits the ultrasonic signal. The transmitted ultrasonic signal is reflected by an object in water, such as a fish or a bottom, and the echo signal is received by the transducer 300. The received echo signal passes through the transmission/reception switching module 200, and then the signal is processed, such as band restriction and amplification by the reception module 400. The processed signal is calculated by the calculation module 500 so as to be displayed, and a predetermined display is then performed by the display module 600. The calculation module 500 typically includes a bottom detection module 51, a bottom-sediment determination module 52, a fish detection module 53, and a fish-length calculation module 54. The display module 600 typically includes a bottom-sediment display module 61 and a fish-length display module 62.
The bottom detection module 51 and the fish detection module 53 calculate positions of fish or bottom based on a time required for the transducer 300 from the transmission of the ultrasonic signal to the reception of the echo signal from the fish or bottom. The bottom-sediment determination module 52 determines a bottom sediment type based on the echo level from the bottom, etc. The determination results for the bottom sediment type includes information, such as the echo level from the bottom itself, the echo level from secondary reflection, temporal variations of these echo levels, a determined bottom sediment type, or the like. The fish-length calculation module 54 calculates a size of the fish (i.e., fish length) based on the echo level from the fish.
FIG. 2 is a display example of a fish finder having such a configuration as described above, such as disclosed in Japanese Unexamined Patent Publication No. 2002-90453. As shown in FIG. 2, the bottom-sediment display module 61 displays predetermined colors associated with the bottom sediment types (from A1 to A4) at the bottom of a display screen based on the bottom sediment types determined by the bottom-sediment determination module 61.
Further, Japanese Unexamined Patent Publication No. 2004-93429 discloses a similar display configuration in FIG. 2 thereof, this display configuration displays colors corresponding to first through Nth echo signals from the bottom are displayed using N blocks on a separate display screen from the display screen on which a shoal of fish are displayed.
Returning to FIG. 2, the fish-length display module 62 displays a symbol representing a fish in a size corresponding to the fish length calculated by the fish-length calculation module 54. The symbol may be colored based on the echo level and may be textured as similar to that of the actual fish. Further, the fish-length display module 62 displays characters, such as a number indicating the fish length in proximity to the displayed fish symbol.
Hereinafter, further referring to FIG. 2, a display example displayed by the display module 600 of the underwater detection device 1 will be explained. In FIG. 2, the vertical axis indicates water depth and the horizontal axis indicates time. Further, because the fish finder transmits ultrasonic signals perpendicularly downward, the display screen is updated one vertical line at a time according to each transmission and reception, while the display screen is scrolled to the left. Thus, the latest data is always displayed at the right end of the display screen.
In FIG. 2, A1 to A4 (i.e., echo images) are displayed by the bottom-sediment display module 61 to display the bottom sediment. The echo images A1-A4 are represented by colors according to the types of the corresponding bottom sediment sections. “B” is a texture displayed by the first fish-length display module 62, and the texture has a size corresponding to the fish length. The texture is an imitation of the fish appearance, and typically is provided with several sizes according to fish length. Further, “C” is a character or number displayed in proximity to the texture B to indicate the fish length. “D” is an echo image of a shoal of fish, “E” is a character or number indicating a water depth, “F” is an echo image of a bottom, and “G” is an echo image of an oscillation line.
However, as mentioned above, the display configuration for the bottom sediment of the conventional underwater detection device only distinguishes the bottom-sediment types by color tone, and a user cannot intuitively distinguish the bottom sediment types only by viewing the display screen. That is, in order to determine the bottom sediment types, the correspondence of the colors to the bottom sediment types must be understood. Further, Japanese Unexamined Patent Publication No. 2004-93429 also discloses a more accurate bottom sediment type determination which can be facilitated by displaying the first to Nth echo signals from the bottom in predetermined display areas and positions. However, this arrangement requires the user's subjectivity or experiences.
Further, for the display corresponding to the fish, the device solely displays the fish texture corresponding to the level of echo signal. Therefore, the determination of fish type requires the user's experiences.